1. Field of the Invention
The present invention, generally, relates to methods of making printed circuit board assemblies using flexible substrates and, more particularly, to a new and improved technique for attaching such flexible substrates to more rigid stiffeners.
Today, as the number of circuits increase so dramatically on a board or substrate, presently existing standards for electrical performance must be maintained, at the very least, to provide both consumer confidence and an increased competitive advantage. A step in this direction has been taken already in the development of the Ball Grid Array for integrated circuit packages, which now is taken to another height by the use of flexible substrates.
The ball grid array packages permit substantial increases in the number of circuit connections per unit area, but now, increases in the power involved have produced heat dissipation problems that are quite real and difficult to solve. Expected solutions require increases in cost, particularly if failures in package performance due to cracks are to be avoided.
2. Description of the Prior Art
U.S. Pat. No. 5,525,834 to Fischer et al. describes a package construction that separates voltage, signal and power leads into different conductive and dielectric layers.
U.S. Pat. No. 5,409,865 to Karnexos describes a package assembling process using a tape automated bonding technique to provide a flexible dielectric film for an area array of pads.
U.S. Pat. No. 5,397,921 to Karnexos describes a grid array tape and a semiconductor are attached to a stiffener by bonding agents to obtain mechanical rigidity.
U.S. Pat. No. 5,386,341 to Olson et al. describes an assembly of a circuit component to a flexible substrate with a rigidizer plate using a low modulus adhesive.